Did you know that you’re only fertile for 6-7 days during your cycle? If you can predict that window of opportunity, you have the power to regulate pregnancy.

That’s right. If you’re like me, you probably grew up thinking that you could get knocked up at any given time. It wasn’t until my early 20s that I learned the truth. I don’t know if this was some monumental crack of information that managed to get by me, if those around me were equally clueless, or if this was some sort of “don’t have sex” scare tactic. But there I was at 23 with no clue about how my hormones work.

As a woman, your reproductive system is completely integrated into your entire body. It has a significant hand in regulating your mental state, your physical state, and can absolutely affect your romantic relationship. Therefore, it’s important to know what’s happening and when!

Start Here

If you aren’t familiar with the basics of women’s hormones or the monthly cycle, I recommend popping back and giving these posts a read first.

Part 1: Sex Hormones For Women 101: If you get to the word “hormone” and are like “whaaaat??”, no problem! Just jump back to the first article in this series to get a basic overview of the 3 primary sex hormones: estrogen, testosterone, and progesterone.

Part 2: Sex Hormones 102: Understanding The Hormonal Cycle For Women: This article outlines how our hormones flow throughout the month and what that means for your moods. Learn what to expect when!

Fertility Awareness Method

Before I get into the rules of fertility, let’s talk about fertility awareness method (FAM). If you’ve never heard of FAM, here’s an overview.

Every cycle, your biometrics repeat. Your basal body temperature, cervical fluid, cervix, and other symptoms (like PMS) all cycle according to your period and ovulation. If you keep close tabs on all of these biometrics, you can predict your fertility cycle with insane accuracy. In fact, after tracking for 13 cycles (over a year), FAM is just as effective statistically as the pill.

I used to think that hormonal birth control was the only reliable way to not get pregnant. Considering the terrible side effects that come with the pill, an implant, or whatever form of hormonal birth control, there’s a large price to pay for pharmaceutical security. And as the science shows, using FAM properly can give you mega power over your body and keep you from getting pregnant when you don’t want to (or get you pregnant faster when you do want to).

So let’s get down to it. What does your fertility cycle look like? And more importantly, when is that little fertility window that could trip you up big time?

Understanding the Fertility Cycle

Your hormone cycle is broken into 2 phases: the follicular phase and the luteal phase. The follicular phase begins with the first day of your period, and the luteal phase begins with ovulation.

The day you ovulate is actually the only day you can conceive. However, sperm can survive up in there for 5-6 days. That means that if you have unprotected sex within 5-6 days before you ovulate, you could get pregnant. This is your fertility window.

So the goal now is predicting that window. If you can know the day you will ovulate, you can know exactly when to use protection.

The 4 Rules of FAM

There are 4 main rules to predicting your fertility window. If you start tracking your metrics using an app like Kindara (which is what I use), it makes it really easy to start seeing trends.

Rule #1

You are generally considered infertile the first 5 days of your period unless your cycle has ever been less than 25 days long.

This is because you aren’t producing cervical fluid to store sperm, and ovulation is more than 5-6 days away. If your cycle has ever been less than 25 days long, you can only consider yourself infertile for the first 3 days of your period.

This is where all the metrics tracking comes into play. You can only follow this rule if you get a clear basal body temp shift at ovulation (~12-16 days before your period starts). Otherwise, there’s no way to be sure you’re not just spotting (which can happen just before ovulation when you’re fertile!) or having irregular bleeding.

Rule #2

If you make it to the evening without producing any cervical that day, you are generally considered infertile. We call this a dry day. Without cervical fluid, sperm can only survive a couple of hours max.

Now, there are a few notes to this rule. If you have sticky cervical fluid for a day or two and go back to no cervical fluid, you are considered infertile the evening of the day without cervical fluid. But if you have creamy or eggwhite-like cervical fluid for a day or two and go back to none, you are not considered safe on that dry day.

Also, natural (your body made it) or synthetic (you bought it) lubricants don’t count as cervical fluid. They don’t provide a place for the sperm to survive.

Rule #3

In the evening of the 4th day after your most fertile cervical fluid once your cervical fluid returns to infertile status if you have had a clear basal body temp shift.

So let’s break this down. Generally, from the first day of your period to ovulation, you’ll have a consistently low basal body temp. The day after you ovulate, your temp will jump up and stay consistently higher until your period. This temperature jump is the first indication that ovulation has happened and you are no longer fertile.

The second thing you’re looking for is your cervical fluid. As you approach ovulation, your cervical fluid will go from sticky to creamy to egg white-like to watery. The day after ovulation, your cervical fluid will start to dry up again.

Once you don’t see any cervical fluid for 3 days and you’ve had a temp shift, you can consider yourself infertile because this is confirmation that ovulation has passed.

Rule #4

If you have had a clear basal body temp shift, you are generally considered infertile the evening of the 3rd day after the shift.

Like we talked about in rule #3, if you see that clear temp shift at ovulation and it stays consistent, you can use that to judge your fertility shift. You can ovulate up to 24 hours after your temp shift, and 10% of the time you can release 2 eggs within 24 hours of each other. So that’s why we give it 3 days before confirming ovulation has passed, and you’re back in an infertility window.

Once ovulation has been confirmed, you are considered infertile for the rest of your cycle.

My Tool Bag

Like I said, I use the app Kindara for my cycle tracking. I also use Daysy as my thermometer and then input my temp data from Daysy into Kindara.

Daysy uses basal body temp to learn your cycle and give a red, yellow, or green light to indicate fertility. While it has accuracy that puts it on par with the pill, I like to be able to see my other biometrics also. It give me more insight into what’s going on in my body. That’s why I take that temp and plug it into my Kindara app.

Kindara allows me to track my cervical fluid, cervix changes, temperature, as well as custom data tracking like whether or not I exercised, had cramps, my sleep data, and log my food. I also have toggles set up to log the color I get from my Daysy. I can use the trends in my data to decide what to eat, how to exercise, when to make social plans, and whether I’m going to need any extra rest. Kindara is free for basic use and $40/year to unlock unlimited metrics tracking to fully customize your log.

Missed Parts 1 & 2? Catch up…

Part 1: Sex Hormones 101 for Women

Part 2: Sex Hormones 102: Understanding the Hormonal Cycle for Women